The invention relates to pistons and more particularly, oil gallery passages in the piston having improved thermal conductivity.
The current trend in the automobile industry is towards increasing the power density of the engine, reducing emissions, and making lighter engines. These requirements lead to a higher thermal load on the engine, especially on the pistons. As a result, the engine, and especially the pistons, experience high temperature. Control of piston temperatures has become one of the determining factors in a successful engine design. Excessive piston temperatures will lead to increased friction at piston-to-bore, piston-to-ring, and piston-to-piston pin interfaces and may result in engine seizure.
Pistons may be cooled by oil jets fired at the underside of the piston's dome. Higher output engines (e.g., turbocharged gas and diesel) typically have an oil gallery designed into the piston dome so that engine oil can be injected into the gallery to facilitate cooling. FIG. 1 shows an example of oil gallery hole 10 cast in a piston 15. Heat reaching the oil gallery during engine operation is conducted away by the oil flowing through it. Approximately 80% of the heat of combustion is removed from high output pistons by means of oil gallery cooling.